Integral ore milling assembly and method of concentration

ABSTRACT

1,046,081. Concentrating ores; ball mills. DENVER EQUIPMENT CO. Jan. 16, 1964 [Nov. 8, 1963], No. 2031/64. Headings B2A and B2H. General description. To a mineral concentrating apparatus adapted to be transported as an integral unit, dry ore in a finely divided state is fed via a conveyer 7, a bin 8 and a conveyer 9 to a jig 10 in which the ore is jigged in a liquid carrier to separate a heavy mineral concentrate and to form a pulp with the remainder of the ore. The pulp overflow is directed via a drum feeder 66 to a rotatable ball mill 11 in which the ore constituents of the pulp are reduced in size and froth flotation reagents are added to the pulp to condition it for flotation. Oversize material is removed by a screen 17 mounted on the discharge end of the mill and is returned to a crusher for further reduction. The conditioned pulp containing the undersize material falls into a sump 18, to which additional reagent can be added, and is fed by a pump 19 to a cone separator 20 where it is separated into a fine fraction which is directed via a vortex overflow pipe 22 to a first froth flotation unit comprising cells 24 to 27, Fig. 2 (not shown) and into a coarse fraction which is directed via an apex underflow pipe 23 to a second froth flotation unit comprising cells 28 to 31. In the cells 24 to 31, the valuable minerals are elevated to the surface in a froth which is skimmed off into a launder 60 for final discharge of the mineral as a concentrate. Tailings from the first bank of cells 24-27 may be delivered to a concentrating table 56&lt;SP&gt;1&lt;/SP&gt; for final removal of valuable minerals before the tailings are discharged to waste. Alternatively, the tailings are fed via a pipe 23a to the second bank of cells 28-31. Below the aerating impellers 57 of the cells 28-31, Fig. 5 (not shown), the cells open into cone separators 32-35 where the non-floated solids from the cells are subjected to a sorting action, the lighter solids being returned to the cells and the heavier ones collecting in the bottom of the cone separators. The tailings from the last cell 31 are directed via a pipe 51 to the concentrating table 56&lt;SP&gt;1&lt;/SP&gt; or are discharged directly to waste. The cone separators have discharge tubing portions 36-39 secured thereto and connected to pipes 40-43 leading to the jig 10. Eccentrics 44 to 47 mounted on a common shaft 48 connected by a belt and pulley to a variable speed drive 50 co-operate with the tubing portions 36-39, Fig. 4 (not shown), to regulate the flow of heavy solids slowly discharging from the cone separators 32-35, the slurry being returned to the jig 10 for recirculation. Ball Mill. The ball mill, Figs. 6 to 9 (not shown), has a cylindrical shell position 61 secured by a trunnion 62 at the feed end and supported near its discharge end by spaced hard rubber rollers 63, 64 mounted on bases 63a, 64a adjustable towards, or away from, each other by means of a bolt and nut 65, 65a. The drum is driven via belts 75, 76 by an assembly comprising a motor 71, Fig. 1 a variable drive 71a Fig. 8 (not shown) and a gear reducer 72 having double output shaft extensions. The drive assembly is mounted on a hinged base 15 to adjust the tension of the belts. The shell portion 61 is lined internally with rubber 67 and is formed with longitudinally extending projections 61c, 61d which serve to elevate the pulp and the grinding balls to aid in the pulp attrition. A grate 69 at the discharge end of the shell has a relatively large central opening 94 for introducing the grinding balls and relatively smaller openings 92 for the discharge of the treated pulp.

April 18, 1967 A. c. DAMAN 3,314,616

INTEGRAL ORE MILLING ASSEMBLY AND METHOD OF CONCENTRATION Filed Nov. 8, 1963 5 Sheets-Sheet l INVENTOR. A rfhur C. Daman ATTORNEYS April 18, 1957 c, DAMAN 3,314,616

INTEGRAL ORE MILLING ASSEMBLY AND METHOD OF CONCENTRATION Filed Nov. 8, 1963 5 Sheets-Sheet 2 A rfhur C. Daman ATTORNEYS A. C. DAMAN April 18, 1967 INTEGRAL ORE MILLING ASSEMBLY AND METHOD OF CONCENTRATION Filed Nov. 8 1963 3 Sheets-Sheet 5 INVENTOR. Arfhur C. Damon BY United States Patent Equipment Company, Denver, Colo., a corporation of Colorado Filed Nov. 8, 1963, Ser. No. 322,422 3 Claims. (Cl. 241-7ll) This invention relates to improvements in apparatus for concentrating minerals and more particularly to apparatus for concentrating minerals using a froth flotation treatment as the primary seperation.

In many mining areas there exist small deposits of valuable mineral which lend themselves to small mining operations having a few workers performing the entire mining and milling procedures. It is customary to mine for short periods of time so as to have available a su fficient supply of ore to keep a mill operating for a long enough interval to produce a substantial amount of concentrate or product.

Present type mills which satisfactorily recover the valuable mineral with small losses have an excessive treatment capacity for such operations and require a variety of equipment placed in a permanent or semipermanent installation which is usually too expensive in original cost and operating expense in comparison to the value of the mineral Which can be produced in such an installation.

It is apparent, therefore, that a complete mill which will efficiently produce valuable minerals at low treatment capacity and is easily transported to small and remote mining operations, and from one operating site to another, has significant utility.

Froth flotation equipment is particularly useful in separating valuable mineral from gangue, such as slimes and failings, and has the advantage of treating a relatively large volume of material in a small space within a short time interval. In the practice of my invention, froth flotation is employed in providing the primary separation of mineral from gangue and other separations are provided to obtain selected or graded products.

In present flotation apparatus employing continuous operation and treating large quantities of ore, there is a considerable quantity of concentrate material which does not respond to flotation effects sufiiciently to carry into the froth and passes from the treatment with the tailing, unless other recovery procedures are provided. This invention utilizes improvements in the concentration apparatus and method of US. Patent No. 3,098,818, owned by the assignee of this application.

The object of this invention therefore is to provide an efiicient and complete milling circuit for a variety of minerals, which is compact in size and arranged as a unitary assembly that can be easily transported to the mine or placer deposit in assembled condition ready for operation at any selected location.

Another object of this invention is to provide apparatus versatile in operation and particularly suitable as complete milling operation for small mining operations.

A further object of this invention is to provide novel control apparatus for selectively controlling the discharge from the cone separator of such a flotation cell.

Yet another object is to provide a novel type of ball mill, particularly suited as a conditioner as well as providing final size reduction of an ore charge.

The practice of the invention will be described with reference to the accompanying drawings, in the several views of which like parts bear similar reference numerals and in which:

FIG. 1 is side elevation view showing the method and 3,314,616 Patented Apr. 18, 1967 apparatus for mineral concentration according to this invention;

FIG. 2 is a top plan view of the assembly shown in FIG. 1;

FIG. 3 is a side elevation view of the assembly;

FIG. 4 is a detailed enlarged view of the eccentric shown in FIG. 1;

FIG. 5 is an enlarged fragmentary view of FIG. 3 showing the lower portion of the flotation cell partially in section;

FIG. 6 is an enlarged side elevation view partially in section of the ball mill shown in FIGS. 1 and 2;

FIG. 7 is a vertical sectional view taken along line 77 of FIG. 6;

FIG. 8 is an enlarged view and front elevation of the mounting for the drive assembly of the ball mill; and

FIG. 9 is a section on line 9-9 of FIG. 6.

Referring to FIGS. 1 and 2 there is shown a single unitary base 5 for supporting the entire assembly according to this invention. A vertical column or beam 6 is attached to the base and supports the elevated end of a conveyor 7 which supplies the ore which has been crushed. An ore bin 8 is attached to the base 5. The bin 8 receives ore from the conveyor 7 and stores it as the supply to the milling operation. A feeder 9 transports the crushed ore from the bin 8 to the mineral jig 10 which is attached to the base. The mineral jig 10' initially separates out coarse free mineral, and a carrier, such as water, is supplied to the jig to produce a pulp containing the remaining ore. The Denver Mineral Jig, for example, will be suitable for this operation.

This pulp is then fed into the ball mill, generally indicated by numeral 11, for final size reduction of the ore charge. The ball mill 1 1 is driven through a belt arrangement by a variable speed drive assembly 13 supported on a hinged base 15 and runs at preselected speeds. Enlarged views of the ball mill are shown in FIGS. 6 and 7, and details of its structure and function will be set forth hereinafter.

The ball mill 11 provides the final size reduction of the ore in the pulp and also conditions the pulp for flotation as flotation reagents can be introduced into the ball mill 11 for mixing with the ore. At the discharge end of the ball mill 11 there is mounted a screen 17 which removes oversize material. The screen rejects may be sorted and oversize material may be returned to the crusher. The screen undersize material falls into the sump 18 located below the screen 17. desired, additional reagents may be added in the sump 18. A pump :19 elevates the pulp through a pipe 2 1 to a cone classifier 20 located on superstructure above the ball mill 11.

In the cone classifier 20, slimes and fine sizes are conducted out the top through a pipe 22. The coarse or spigot product comes out the bottom through a pipe 23.

The flotation unit is illustrated as having eight cells numbered 24 to 31, inclusive (FIG. 2). The first four cells 24 to 27, viewed from left to right, receive the pulp containing fine sizes through a feed pipe 22 and the last four cells 28 to 31 receive the coarse product through another feed pipe 23. The last four cells 28 to 31 have separator cones 32 to 35 mounted in openings below their respective impellers, although only one or any plurality of cones may be provided in such cells. Flotation cells with separator cones of the type described in the U8. Patent No. 3,098,818 would be suitable for the last four cells 28 to 31. However, the preferred flotation cells have a particular relationship between the diameter of the impeller and the top opening in the separator cone which is more fully shown in FIG. 5 and later described.

Each of the separator cones 32 to 35 has flexible tubing portions 36 to 39 secured to the lower extremities respectively thereof which are coupled respectively to pipes 40 to 43 leading to the mineral ji g 10. Adjacent and in intermittent or selective contact with each flexible tube are eccentrics 44 to 47, respectively. Each eccentric is drivably connected to a common control shaft 48 which extends lengthwise of the flotation cells. The control shaft 48 is connected to a pulley 49 which is belted to a variable speed drive 50, preferably using a drive motor and a speed reducer.

' Each eccentric 44 to 47 and corresponding adjustable backing supports (not shown) restrict the cone discharge from its associated flotation cell and may be disposed to curtail all flow when desired. The normal arrangement of the eccentrics is to have one cone emptying and the others closed with the speed of the shaft determining the flow through the flexible tubing connection. This control provides very close regulation of small amounts of liquid and mineral going through the cone which is very important in smaller mill operation due to the small quantities of ore being handled and the treatment time required to collect desired mineral in the cone. By selectively closing the flexible tube the mineral can collect in the bottom of the separator until a quantity suflicient for ultimate disposal is accumulated. In addition, the single drive arrangement for the plurality of eccentrics can be controlled so that when the drive is stopped all of the flexible passages will be substantially or entirely closed by adjusting the backing support to prevent solids from descending and passing through the cone which might otherwise be returned to flotation. Then in starting operation the flexible passages will be substantially or entirely closed until a desired accumulation exists in the cone.

The detailed construction of the eccentrics 44 to 47 with corresponding backing supports are shown in FIG. 4, which shows eccentric 44 in detail. The eccentric 44 is mounted on control shaft 48 and has an inner hub portion 52 suitably fastened to shaft 48 as for example by keying. An outer eccentric member comprising two concentrically disposed rings 53, 54 having arranged therebetween a plurality of rollers 55 in a manner similar to a roller bearing rests over hub portion 52. Upon rotation of shaft 48 oscillatory movement is imparted to ring 54 to vary the passage of flexible tube 36. The eccentric is easily removable and can be replaced by another eccentric of a different size. The eccentric feature allows flexibility in the amount of closure on each flexible tube and facilitates convenient replacement thereof. Each eccentric and flexible tube combination has a corresponding saddle-shaped backing plate illustrated by numeral 56. Backing plate 56 extends around tube 36 for suitable coverage as for example about 120 and supports flexible tube 36 against the horizontal force imparted by eccentric 44. A slotted portion 57 suitably arranged on the back of plate 56 provides a means for adjustably fastening it to a support bar 58 with a nut 59. This adjustable feature allows horizontal movement of backing plate 56 against flexible tube 36 to slightly restrict or completely close the passage of flexible tube 36 as required.

The mineral jig is located below the flotation cells 32 to 35 and receives coarse products from the cones in a gravity flow, with heavier mineral concentrated and retained in the jig while the remainder of the circulating flow is passed on to the ball mill for further grinding.

In the flotation cells 24 to 31 the mineral is subjected to a sorting action elevating the valuable mineral to the surface where it collects in a froth which is removed by mechanical skimmers (not shown) and discharged into a launder 60 (FIG. 2) for final discharge from the treatment as concentrate or product.

Tailings passing from the final flotation cell 31 discharge through a pipe 51 and are delivered as feed to concentrating table 56 supported on base 5. This table acts as a scavenger for final removal of mineral before the tailings are discharged. If the tailings do not carry enough mineral the concentrating table 56 can be omitted with the tailings discharged to waste.

Referring to FIG. 5 there is shown in more detail the preferred construction of flotation cells 28 to 31 which have a control of cone separator discharge. An opening is provided in the bottom of each cell and the diameter of the upper end of the cone separator 35 is of substantially greater diameter than the impeller 57 and approximately the diameter of the impeller cover 58. This larger opening allows more solids to descend into the cone but by having a flexible outlet member 36 and the novel eccentric control and backing support previously described, descending material is retained in the cone or its outflow so restricted as'to retain a bed of solids subject to the sorting effect of the centrifugal action of the impeller on the open end of the cone. In this action, heavier solids descend and displace lighter functions, at least some of which ascend into the cell and either float or pass with the tailings according to their flotation characteristics.

When a flotation cell is placed in continuous operation, there is a tendency for some of the concentrate material to remain suspended near the bottom of the cell and not respond to the aeration. This may be due to inadequate conditioning or other causes and over a period of time builds up a zone of high density material near the bottom which material wanting to float has difficulty in penetrating.

The provision of a cone of the type shown in FIG. 5 underneath the impeller provides escape for such material. Much of it is drawn onto the cone and subjected to the sorting action therein. Another part is swept and dissipated by the upcast flow from the cone permitting relatively uniform densities to be maintained throughout the vertical extent of such cells. Consequently, such a flotation cell produces maximum flotation effect throughout a long period of continuous operation.

Referring again to the circuiting arrangement shown in FIGS. 1 and 2, the conditioned pulp in fine sizes passing from separator 20 through line 22 to the first bank of cells floats readily and the tailings from this separation can be passed to the scavenger concentrating operation on table 56 before they are discharged as waste, or optionally may be passed to the second bank through pipe 23a. While the coarser feed from separator 20 to the second bank of cells does not float as readily, the functioning of the cones to extract mineral from the pulp supplements this flotation action to such an extent that the final tailings discharged into line 51 are also taken as feed to table 56.

The jig 10 extracts heavier mineral, such as free gold, or other high grade concentrate, while the remainder of the feed to jig 10 is discharged as feed to mill 11. While this closed circuit operation has a substantial circulating load, the recirculated fraction is an upgraded material, the concentrate portion of which responds readily to flotation separation after a second stage conditioning. Consequently, the overall recovery of such a milling circuit is relatively high.

Referring to FIGS. 6 and 7, there is shown in more detail the novel structure of the mill assembly inclusive of ball mill 11. Ball mill 11 includes interconnected end sections and an intermediate section formed as a cylindrical shell portion 61 flanged at both the intake and discharge ends and having a flanged trunnion portion secured by a trunnion 62 at the feed end and the mill is supported near its discharge by structure 12 having rollers 63 and 64 of flexible material such as hard rubber in immediate contact with shell portion 61. The bases of rollers 63 and 64 are positioned on each side of cylindrical shell portion 61 (see FIG. 7) and are simultaneously adjustable toward or away from the center of shell portion 61 by a single bolt 65 having threads on each end thereof. The other end section comprises the screen 17 having a flanged end 61b of a diameter sub stantially the same as the shell portion 61 which is detachably connected to the flanged end of the shell as hereinafter described.

A drum feeder 66 is mounted on the feed head of mill 11 to pass pulp from jig to mill 11 (FIG. 1). Supported on intermediate support 12 and below ball mill 11 is a variable speed drive assembly 13 which comprises a motor 71, a variable drive such as a Reeves Variable Drive 71a, and a gear reducer 72. Gear re ducer 72 has double shaft output extensions 73 and 74 each belted by a plurality of belts 75 and 76. The belts 75 and 76 can rest directly on the cylindrical shell portion 61 in a flat drive relationship or have sheaves on shell portion 61 depending on the speed range and the speed ratio between the shaft extensions 73 and 74 and the diameter of shell portion 61.

The hinged base for adjusting the tension in belts 75 and 76 is more fully illustrated in FIG. 8. Drive assembly 13 is mounted on base 15. Base 15 is attached at one end of support 12 by a hinge 81. The other end of base 15 is attached to support 12 by the combination of flange 82, eyebolt 83 and nut 84. Flange 82 is attached to the support 12 with eyebolt 83 extending through flange 82 and secured thereto with a nut 84 so that adjustment of nut 84 adjusts vertically base 15 and ultimately the tension in belts 75 and 76.

By having drive assembly 13 mounted below the ball mill 11, the tension in the belts 75, 76 can be conveniently adjusted and remains constant and avoids slippage.

The cylindrical shell portion 61 is lined with a flexible material 67 such as rubber or the like, to protect the shell from deterioration due to the continued movement of the pulp and grinding balls therein (FIG. 6). Shell 61 has a flange portion 61a at the feed head which is 'bolted to the head to allow its quick removal for relining of the flexible material or replacement with another length of shell 61. Shell 61 has a flange portion 61b at the discharge head with flexible material 67 extending over portion 61b. A cylindrical extension 68 extends past shell 61 and also has a flange portion 68a. Discharge grate 69 has a tapered end portion 69a disposed between flange portions 61b, 68a. A bolt 70 extends through flange portions 61b, 65a, to secure discharge grate 69. Lifters 61c and 61d are projections or upstanding portions on the inner surface of shell portion 61 which run lengthwise of the mill. The function of lifters 61c and 61a is to elevate the pulp and ball charge to aid in the attrition effect in the mill.

The structure of the discharge head of the ball mill 11 is more fully shown in FIG. 9. The discharge head member of ball mill 11 is open and has discharge grate or partition portion 66 having a plurality of small openings 92 around the outer periphery. These openings 92 may be slots or holes of a size suitable to freely discharge the pulp and contain the ball charge. A central opening 94 of a diameter slightly greater than the grinding balls 93 is provided in end grate portion 91 for charging of grinding balls 93. The pulp indicated by dotted lines 95 is discharging at a level substantially below opening 94. This arrangement therefore provides a substantially open ended ball mill which facilitates the quick passage of the pulp in the mill, thus avoiding overgrinding.

While the apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus and that changes may be made without departing from the scope of the invention which is defined in the appended claims.

I claim:

1. A mill assembly for wet grinding an ore pulp comprising a base having a trunnion support means at one end of the mill and a pair of spaced roller support means at its opposite end, said mill including interconnected end sections and an intermediate section formed as an elongated cylindrical shell flanged at both the intake and discharge ends, one said end section comprising a head member at the intake end of the shell having a flanged trunnion portion abutting a flanged end of the shell and forming a feed inlet to the shell and the other said end section having a peripheral screen portion at the discharge end of the shell over which the mill discharge passes and having a flanged end of a. diameter substantially the same as the shell and abutting a flanged end of the shell, said shell supported for rotation by said roller means adjacent the screen member, and said head member supported for rotation by its trunnion portion for rotation of the shell about a substantially horizontal axis, said pair of roller means adjustable in a horizontal plane below the shell toward and away from the center of the shell by a common threaded member, said shell having a flexible liner bonded to its inner surface, an apertured partition member at the discharge end of the shell having a central opening of greater diameter than grinding media introduced therethrough and a plurality of openings of smaller diameter than the grinding media disposed in a circumferential pattern to pass ground ore through the discharge end of the shell and retain the grinding media in the shell, an end portion of the shell liner and said partition member being clampingly secured between the abutting flanges of the shell and the discharge end section, fastening means for detachably interconnecting said abutting flanged portions so as to permit removal of the shell and associated liner for replacement or repair thereof, drive means for rotating the mill including a motor and gear reducer, the gear reducer having a double end shaft output, at least one belt extending from each shaft of the gear reducer around the shell adjacent the trunnion end of the mill, and a support for the motor and gear reducer having one end pivotally attached to the base to pivot under the weight of the motor and gear reducer to adjust the elevation of the shafts to vary the tension in the belts.

2. A mill assembly as set forth in claim 1 wherein the inner surface of said shell includes a plurality of spaced upstanding portions formed therein extending its lengthwise extent which the liner covers to form lifter means for elevating the ore in the shell during its rotation.

3. A mill assembly as set forth in claim 1 wherein the drive means is supported below the shell and said belts extend upwardly around the shell.

References Cited by the Examiner UNITED STATES PATENTS 642,123 1/1900 Hoffman 308-203 X 1,848,391 3/1932 Simpson 204--213 1,891,995 12/1932 Marcy 308-203 X 2,058,257 10/1936 Porteous 241-182 X 2,078,829 4/1937 Barratt 241178 2,396,057 3/1946 Peterson 241176 X 2,463,683 3/1949 Fay 51-164 X 2,549,919 4/1951 Moller 241-70 X 2,812,541 11/1957 Webster 241-182 X 3,027,746 4/ 1962 Smith 74242.15 X 3,107,867 10/1963 Svensson 241-183 X 3,216,666 11/1965 Svensson 241-176 WILLIAM W. DYER, JR., Primary Examiner. H. F. PEPPER, JR., Assistant Examiner. 

1. A MILL ASSEMBLY FOR WET GRINDING AN ORE PULP COMPRISING A BASE HAVING A TRUNION SUPPORT MEANS AT ONE END OF THE MILL AND A PAIR OF SPACED ROLLER SUPPORT MEANS AT ITS OPPOSITE END, SAID MILL INCLUDING INTERCONNECTED END SECTIONS AND AN INTERMEDIATE SECTION FORMED AS AN ELONGATED CYLINDRICAL SHELL FLANGED AT BOTH THE INTAKE AND DISCHAGE ENDS, ONE SAID END SECTION COMPRISING A HEAD MEMBER AT THE INTAKE END OF THE SHELL HAVING A FLANGED TRUNNION PORTION ABUTTING A FLANGED END OF THE SHELL AND FORMING A FEED INLET TO THE SHELL AND THE OTHER SAID END SECTION HAVING A PERIPHERAL SCREEN PORTION AT THE DISCHARGE END OF THE SHELL OVER WHICH THE MILL DISCHARGE PASSES AND HAVING A FLANGED END OF A DIAMETER SUBSTANTIALLY THE SAME AS THE SHELL AND ABUTTING A FLANGED END OF THE SHELL, SAID SHELL SUPPORTED FOR ROTATION BY SAID ROLLER MEANS ADJACENT THE SCREEN MEMBER, AND SAID HEAD MEMBER SUPPORTED FOR ROTATION BY ITS TRUNNION PORTION FOR ROTATION OF THE SHELL ABOUT A SUBSTANTIALLY HORIZONTAL AXIS, SAID PAIR OF ROLLER MEANS ADJUSTABLE IN A HORIZONTAL PLANE BELOW THE SHELL TOWARD AND AWAY FROM THE CENTER OF THE SHELL BY A COMMON THREADED MEMBER, SAID SHELL HAVING A FLEXIBLE LINER BONDED TO ITS INNER SURFACE, AN APERTURED PARTITION MEMBER AT THE DISCHARGE END OF THE SHELL HAVING A CENTRAL OPENING OF GREATER DIAMETER THAN GRINDING MEDIA INTRODUCED THERETHROUGH AND A PLURALITY OF OPENINGS OF SMALLER DIAMETER THAN THE GRINDING MEDIA DISPOSED IN A CIRCUMFERENTIAL PATTERN TO PASS GROUND ORE THROUGH THE DISCHARGE END OF THE SHELL AND RETAIN THE GRINDING MEDIA IN THE SHELL, AN END PORTION OF THE SHELL LINER AND SAID PARTITION MEMBER BEING CLAMPINGLY SECURED BETWEEN THE ABUTTING FLANGES OF THE SHELL AND THE DISCHARGE END SECTION, FASTENING MEANS FOR DETACHABLY INTERCONNECTING SAID ABUTTING FLANGED PORTIONS SO S TO PERMIT REMOVAL OF THE SHELL AND ASSOCIATED LINER FOR REPLACEMENT OR REPAIR THEREOF, DRIVE MEANS FOR ROTATING THE MILL INCLUDING A MOTOR AND GEAR REDUCER, THE GEAR REDUCER HAVING A DOUBLE END SHAFT OUTPUT, AT LEAST ONE BELT EXTENDING FROM EACH SHAFT OF THE GEAR REDUCER AROUND THE SHELL ADJACENT THE TRUNNION END OF THE MILL, AND A SUPPORT FOR THE MOTOR AND GEAR REDUCER HAVING ONE END PIVOTALLY ATTACHED TO THE BASE TO PIVOT UNDER THE WEIGHT OF THE MOTOR AND GEAR REDUCER TO ADJUST THE ELEVATION OF THE SHAFTS TO VARY THE TENSION IN THE BELTS. 